1. Field of the Invention
The present invention relates to an exposure apparatus exposing a substrate to light and particularly relates to an exposure apparatus including a vacuum pump which evacuates the interior of the exposure apparatus.
2. Description of the Related Art
Exposure apparatuses that project a circuit pattern written on a reticle (mask) on a wafer or the like through a projection optical system have been used to manufacture a minute semiconductor element including a memory, a logic circuit, and so forth.
The minimum critical dimension (resolution) that can be transferred through the exposure apparatus is proportional to the wavelength of light used to perform an exposure and is inversely proportional to the numerical aperture (NA) of the projection optical system. Therefore, the wavelength of light used to perform an exposure has become increasingly shorter in accordance with the need for micro-miniaturizing the semiconductor element. Then, exposure apparatuses using extreme ultra-violet (EUV) light having a wavelength of from 10 nm to 15 nm or around (EUV exposure apparatus) have been developed so as to transfer a minute circuit pattern having a length of 100 nm or less with efficiency.
EUV light is easily attenuated by gas, and induces a photochemical reaction between an impurity including carbon and oxygen so that a carbon compound is adhered to an optical element. According to the EUV exposure apparatus, therefore, an exposure is performed in a vacuum environment.
When using a vacuum pump so as to evacuate the interior of the exposure apparatus, the temperature of each of other elements included in the exposure apparatus is changed due to heat generated and/or absorbed by the vacuum pump so that the circuit pattern may be transferred with a decreased precision. Particularly, it is difficult to use a material with a small linear expansion coefficient, which is used for a mirror, for a barrel holding the mirrors of a projection optical system and/or a structure provided with a position measuring unit arranged therein. Therefore, an unallowable position shift may occur due to a little temperature change so that the circuit patterns may be transferred and overlaid with a decreased precision.
The following configurations have been proposed to reduce an influence caused by heat generated and/or absorbed by a vacuum pump.
According to Japanese Patent Laid-Open No. 2005-353986, a cryo panel (cryo pump) and an electric-field trap panel are provided near a mirror and the temperature of the mirror is adjusted through the electric-field trap panel so that a thermal influence exerted by the cryo panel is reduced. According to Japanese Patent Laid-Open No. 2005-101537, a shield is arranged so as to surround a cryo panel arranged in a projection optical system, so as to reduce a thermal influence exerted by the cryo panel on the mirror. Further, the temperature of the shield and/or the cryo panel is controlled so that the temperature of the mirror is controlled and kept in a predetermined range.
According to Japanese Patent Laid-Open No. 2005-353986, the degree of vacuum around the mirror is increased through the cryo panel. However, since the electric-field trap panel is arranged so as to be opposed to the cryo panel, the absorption efficiency achieved by the cryo panel is decreased. Namely, for achieving the same degree of vacuum as that achieved in the case where no electric-field trap panel is provided, a large-sized vacuum pump should be arranged. If the size of the vacuum pump is increased, an increased thermal influence is exerted on members other than the mirror, such as a barrel.
Since the shield is also arranged to surround the cryo panel according to Japanese Patent Laid-Open No. 2005-101537, the absorption efficiency achieved by the cryo panel is decreased. Consequently, the same problem as that disclosed in Japanese Patent Laid-Open No. 2005-353986 occurs.
Further, the temperature of the mirror is changed not only by a change in the temperature of the vacuum pump, but also by an exposure. Therefore, when the temperature of the shield is controlled based on a result of the measurement of the mirror temperature for changing the shield temperature so as to reduce a thermal influence exerted by the vacuum pump, the controlled temperature may become a thermal disturbance for members other than the mirror, such as the barrel. Further, if the vacuum pump and the shield are arranged in different directions with reference to members other than the mirror, such as the barrel, a temperature distribution may occur in a member such as the barrel so that the member is deformed.